Strange colour crab claw

[Paleonique]

A couple of hours in on our fossil hunt at Glen Afric, I spotted another crab fossil! This had now been our 3rd crab of the day.

We have not found a similar crab to this one. Any ideas or thoughts on why the colour is so strange?

 

 

 

[Doctor Mud]

There is a lot of variation in the colour of the fossil crab shell at this site. It varies from pale yellow to pink todark brown.

The process of a fossil forming often involves replacing the original building blocks of an animal (crab shell in this case) with other minerals. At this site the crabs get encased in concretions after they die due to a reaction between the decomposing crab and the sediment. 

There is a lot of variation - soft concretions and hard concretions, many colours of fossil shell. I’m speculating here. But I imagine that mineral solutions in the rock could seep into concretions and infuse fossil crab shell with minerals such as iron. 

 

So different colours reflect processes that have happened since the crab died, was fossilised and eroded out the cliff. Hope this helps!

 

This one looks like a soft concretion (can you scratch the rock with s knife?) The crab shell is often this colour in softer concretions.

 

 

[RJB]

To add to what @Doctor Mud has said,,,  color can also be different on what crab material is 'exposed' to what is inside the concretion.   Nice lookin little crab conc though. 

 

RB

[Doctor Mud]

18 hours ago, Paleonique said:

This had now been our 3rd crab of the day.

This one is a little beauty by the way. Looks like the whole crab will be inside. That is probably the large claw and the smaller claw is hidden in the rock.

You can see the legs behind the claw.

 

Love to see the others!

[Paleonique]

16 hours ago, Doctor Mud said:

There is a lot of variation in the colour of the fossil crab shell at this site. It varies from pale yellow to pink todark brown.

The process of a fossil forming often involves replacing the original building blocks of an animal (crab shell in this case) with other minerals. At this site the crabs get encased in concretions after they die due to a reaction between the decomposing crab and the sediment. 

There is a lot of variation - soft concretions and hard concretions, many colours of fossil shell. I’m speculating here. But I imagine that mineral solutions in the rock could seep into concretions and infuse fossil crab shell with minerals such as iron. 

 

So different colours reflect processes that have happened since the crab died, was fossilised and eroded out the cliff. Hope this helps!

 

This one looks like a soft concretion (can you scratch the rock with s knife?) The crab shell is often this colour in softer concretions.

 

 

Once again, thank you so much for the information. I appreciate it very much! 

Yes, It is a soft concretion and can be easily scratched by a knife. 

[Paleonique]

14 hours ago, RJB said:

To add to what @Doctor Mud has said,,,  color can also be different on what crab material is 'exposed' to what is inside the concretion.   Nice lookin little crab conc though. 

 

RB

I'm already learning so much! Thank you for the information

[mamlambo]

That's a very good looking crab @Paleonique! It should prep out nicely. Most of the crabs at Glenafric are the Tumidocarcinus Giganteus crabs but there are a few other species out there. One of them is very rare and not yet described I think. It has a square shaped body, so keep a look out for those